model building for reference projections

[Adam Frost]

I am a new member of the 3dem list. We are working on a large,
pseudo-helical filament imaged in ice. We are struggling to index the
helical lattice and determine the selection rule, as the FFT only has layer
lines out to ~25 Ang from raw images. However, we think we know what the
helical symmetry should be, both from what we know about our protein and
from features in the FFT. 

I would like to build a 3D model of our expectations, in order to calculate
projections and transforms, and then to test our assumptions by comparing
the expected and observed ffts. I have no idea which software package would
be best suited to building such a model, projections from it, or transforms
of those projections. Any suggestions will be greatly appreciated. 

Many thanks, --Adam